In an offshore structure installation such as a jacket installation or a wind turbine structure installation, a subsea grout seal is typically utilized to seal an annular gap between a sleeve structure inner surface and an outer surface of a tubular structure, such as a pile or a supporting leg, inside the sleeve structure against a high column of concrete during the grout hardening period. FIG. 1 illustrates a deepwater offshore platform with extended legs from water surface to sea floor and a plurality of pile sleeves for housing piles. As shown in FIG. 1, an offshore platform deck 1 is supported by a jacket 2 extended from water surface 6 to sea floor 5. A plurality of pile sleeves 4 are attached to the bottom of the extended legs to house a plurality of piles 3, which are driven into sea floor 5 to provide the anchoring to the platform. Grout seals are installed at the bottom of sleeve 4 inner surfaces.
Offshore platform installations have had more than 60 years' history. Acceptable pile offsets, or acceptable annular gaps between a sleeve inner surface and a pile outer surface during pile driving, have been gradually developed and standardized in the industry. The typical maximum annular gap for a deepwater jacket is about 2˜3 inches (about 51˜76 mm). A gap size of an inflatable packer for a jacket installation usually refers to the width between a packer inner surface before and after a grouting operation. For a passive grout seal, the gap usually refers to the width between steel annular structure inner surface, such as a planar annular plate inner surface, and the pile outer surface.
For an offshore jacket installation, a subsea grout seal is usually located at the bottom of a pile sleeve 4 inner surface near sea floor, below a plurality of pre-installed tapered guide shim plates. The seal has to be rugged and highly reliable because any seal failure such as grout leaking could cause the connection failure between a pile sleeve and a pile. Consequently, it could result in the foundation failure of the platform.
An offshore wind turbine structure is usually composed of two parts: 1) the upper part comprising a generator and turbine blades, and 2) the bottom part including a structural support base including a single leg base or a multi-leg base with multiple supporting legs. FIG. 2 illustrates an offshore installed wind turbine structure 7 with a generator 9 and a plurality of turbine blades 8 supported by a multi-leg base 10. In this configuration, a sleeve structure is individually driven into seabed 5 and serves as a sleeve 4 above water surface 6 for housing each supporting leg of the multi-leg base 10. A grout seal is typically installed at the bottom of each supporting leg outer surface, which is different from the offshore jacket installation mentioned earlier. Because there are no pile driving activities during wind turbine structure installation, no mud wiper is needed. In addition, offshore wind turbine structure installations usually occur in a shallow water area with smaller waves than in deepwater during installations, as well as less wave induced dynamic motions between installed sleeves 4 and supporting legs of a multi-leg base 10.
Because each sleeve 4 is individually driven, desired dimensional control between any two driven sleeves 4 is very difficult to achieve. As a result, the allowable gaps between one sleeve 4 inner surface and one inserting leg 3 outer surface will certainly become much larger than the gaps typically used for an offshore jacket installation mentioned earlier. To be specific, the resultant gap width can be as wide as one foot (about 300 mm). No existing subsea grout seals are able to handle such large gaps.
Existing Grout Seals for Offshore Jacket Installation
Until recently, most subsea grout seals have been designed only for offshore jacket installations. And in general, there are two types of grout seals for pilings in offshore jacket installations: 1) an active type such as an inflatable packer, and 2) several passive types such as a CRUX grout seal or a mechanical grout seal.
Inflatable Packer for Offshore Jacket Installation
Inflatable packer was introduced to offshore industry in the 1970's and it has been widely utilized in offshore platform installation fields since then. Today, inflatable packers still occupy a very large grout seal market share, especially in deepwater jacket installation applications. Inflatable packer is an active device employing a control system and a power system located above water to activate the seal during grouting operation by injecting high pressure air to perform the grout sealing function. FIG. 3 is an ISO cross section view of a typical inflatable packer used as a subsea grout seal. As an active seal, the seal element is in a retracted position without a contact between the packer inner surface and a pile outer surface during pile inserting, lowering, and driving. As shown in FIG. 3, an inflatable packer element 11 is fixed to the inner surface of a sleeve 4 in a non-inflated condition, and an air injection tubing 12 is attached at the outer surface of the sleeve 4. To prevent mud at sea floor from polluting the annulus space during pile driving, a mud wiper 14 is usually installed below the packer element 11.
All subsea grout seals utilized for offshore jacket installation have two distinguished operational sections throughout a jacket installation process. Each section has its main concerns for potential damages to grout seals. For example, the first section is for various activities before grouting action, such as pile inserting, lowering and driving. The second section is for a grouting action. The uniqueness of the above-mentioned inflatable packer system is its configuration in the first section, in which the packer element 11 is in a retracted position to avoid any contact with the pile. However, the second section is a problematic one to cause some system reliability concerns. To be specific, such concerns include potential damages of a long-distance and high-pressure piping subsystem, and malfunction of the complicated control subsystem and the power package. In addition, an inflatable packer assembly has a significant higher cost than existing passive grout seals due to high costs in assembly fabrication, yard installation and yard testing.
Passive Seals for Offshore Jacket Installation
A typical passive seal is CRUX annular grout seal, which has an outer head portion attached at a sleeve inner surface and a bulbous ring functioning as the sealing element. FIG. 4A illustrates a CRUX annular seal element 20 prior to piling activities. As shown, a plurality of pre-installed tapered guide shim plates 16 are attached to the inner surface of a sleeve 4 above the CRUX grout seal. An outer head portion 18 is fixed to the sleeve 4 inner surface with an inside cavity 19. A bulbous ring 22 with a fiber core forms a sealing element during grouting. The inner diameter of the bulbous ring 22 is less than the outer diameter of a pile so that the deformed bulbous ring 22 produces compression force against the pile 3 outer surface to perform a grout sealing function and also functions as a mud wiper during pile inserting, lowering and driving. FIG. 4B is a partial cross-section view of a CRUX annular seal when a pile 3 is driven through and a column of grout 13 is poured through the annulus between a pile 3 outer surface and a pile sleeve 4 inner surface. As shown in FIG. 4B, the bulbous ring 22 is deformed and the annular seal element 20 is bended against the pile 3 outer surface in a vertical orientation, which has several levels of shear keys 21, to perform the grout sealing action against the poured column of grout 13.
A passive seal is significantly less expensive than an inflatable packer. However, the common concerns for passive seals are the protection and the reliability of the seals first section during the offshore installation in terms of pile inserting, lowering and pile driving. The pile 3 bottom outer sharp edge could work as a knife to damage the resilient rubber section between the bulbous ring 22 and the outer head portion 18 due to dynamic heave motions of a pile 3 during its lowering and inserting.
It should also be pointed out that a traditional mechanical grout seal is another type of passive seal. Traditional mechanical grout seals are usually used only for shallow water applications because it could not take potential dynamic loading from shear keys which are commonly welded both on the pile top outer surface and on the sleeve inner surface of a deepwater jacket for increasing the concrete bonding strength between a sleeve and a pile. FIG. 5 illustrates an ISO cut-off section view of a typical mechanical seal with a driven pile and a column of grout poured in the annulus between a pile 3 outer surface and a pile sleeve 4 inner surface. As shown in FIG. 5, an elastic seal element 23 is an annular rubber tubular with an inner diameter less than the outer diameter of the pile 3. A plurality of curved steel strips 24, running through and bonded with the elastic seal element 23, slide upward through the fixed rings 25 when compressed. The steel strips 24 fixed at the bottoms 26 are also attached at the sleeve 4 inner surface. The elastic seal element 23 produces a grout sealing force, through the rubber restoring force due to the compressed elastic seal element 23 and the compressed steel strips 24 during pile inserting, against the poured column of grout 13 between the pile 3 outer surface and the inner surface of the sleeve 4. A plurality of pre-installed tapered guide shim plates 16 are above the seal element 23. Moreover, the seal element 23 also prevents the mud pollution from entering the sealed chamber during pile 3 driving.
Based on the discussion above, every type of grout seal requires one type of external force to perform its sealing action during a grouting operation. So far, only two types of external forces have been utilized for all existing grout seals in the offshore industry: 1) external high-pressure air as in the case of active grout seals; and 2) restoring force induced by deformed rubber elements during pile inserting and lowering. However, each of such types of the external force has its pros and cons in their field applications. The selection of which type external force as its sealing action force for each type grout seals is a critical factor to determine the grout seal overall reliability and the grout seal overall costs. Based on records of offshore jacket installations, inflatable packer type grout seals have the highest level of overall reliability compared with passive grout seals. However, they are also much more expensive than passive grout seals.
In August. 2014, the inventor of this disclosure first disclosed a third type of external force for grout sealing action in a new type of passive grout seal in U.S. Pat. No. 9,677,241 to Lee, issued on Jun. 13, 2107. In that patent, an annular elastomeric bag was utilized to perform a grout sealing function between a pile sleeve inner surface and a pile outer surface with the help of this third type of external force derived from the poured grout gravity force. In an underwater condition, the density difference between typical grout with density around 1.92 g/cm3 and sea water with a density around 1.05 g/cm3 shall be able to perform, with the help of a high pressure force inside the annular elastomeric bag during grouting operation, two grout sealing functions: 1) the vertical high pressure force acting at the elastomeric bag bottom over an annular gap performs the grout sealing action over the annular gap, and 2) the horizontal high pressure force, with the same magnitude as the vertical high pressure force because both grout and seawater are fluid, acting at the annular elastomeric bag inner surface against the pile outer surface to achieve the sealing effect between the pile outer surface and the sleeve inner surface.
In May 2017, two improvements were disclosed in U.S. Pat. No. 9,970,171 to Lee, issued on May 15, 2018, as the continuation-in-part of the above-mentioned patent. The first improvement was to add one planar ring plate or one cone shape ring plate to a sleeve inner surface below an annular resilient elastomeric bag. The purpose of adding the planar ring plate is to reduce the annular gap width and to let the planar ring plate take a large portion of the poured grout induced gravity loading away from the annular resilient elastomeric bag bottom. The purpose of adding a cone shape ring plate is similar to adding one planar ring plate, and, moreover, the cone shape ring plate can be combined with the bottom rubber band section to perform a plugging action to further enhance the sealing effect, because the added plate can take up the majority of grout induced loading. Moreover, this new addition makes it possible to greatly reduce the rubber band thickness of the annular elastomeric bag as well as the weight of the elastomeric bag. Such weight reduction not only reduce the fabrication cost of the grout seal, but also facilitate the transportation and site installation of the grout seal.
The second improvement was localized reinforcement of the annular elastomeric bag over the annular gap. Due to the weight reduction of the annular resilient elastomeric bag, most of the elastomeric bag rubber band thicknesses becomes very thin, and so the band section of the thin layer over the annular gap could be bulged out with a local stress concentration. This additional localized reinforcement is achieved by adding one annular bandage layer at the bottom inner surface of the elastomeric annular bag over the location of the annular gap. Because it is localized reinforcement, the increased weight of the elastomeric bag is limited. In addition, the localized reinforcement annular band section can be combined with the cone shape plate to perform a plugging action for grout sealing. This plug assisted grout sealing is a different grout sealing action for the annular gap compared with the conventional bulging based sealing action for the annular gap. In other words, the grout seal configuration based on the above two improvements can bring up two independent grout sealing actions to further enhance the overall system reliability.
The selected third external force for grout sealing in the above mentioned patents has three key advantages over the two existing external forces for grout sealing, as follows:
1) The gravity based external pressure force, namely, gravity differential pressure force, comes from a very reliable source without a need for any external power input as in the case of inflatable packers. Such force eliminates all potential sources for harmful results known to the offshore industry, not only for active grout seals but also for passive grout seals. Therefore, such gravity differential pressure force based grout seal shall have significantly higher system reliability than any existing grout seal;
2) The magnitude of the gravity differential pressure force depends solely on two factors: grout density and grout column height. Unlike the external force utilized by an inflatable packer, the gravity based external force is independent of water depth. Based on one conventional deepwater jacket sleeve-to-pile configuration, the magnitude of the gravity differential pressure force shall be sufficient to perform the two grout sealing functions mentioned earlier, as illustrated in the following example: one 84″ O.D. pile inside one 90″ I.D. sleeve with one foot (about 300 mm) tall band section for one annular resilient elastomeric bag, a grout column height of 30 feet (about 9.1 m, typical designed grout column heights ranging between 25˜40 feet) and a maximum gap width of 3″ (about 76 mm). In this configuration, the total vertical pressure force reaches around 4 S. Tons (about 3.6 M. Tons) at the elastomeric bag bottom over the annular gap width and the total horizontal pressure force, acting at the resilient elastomeric bag inner surface against a pile outer surface, reaches over 18 S. Tons (about 16 MT). Test results confirmed that the minimum required grout column height for a grout sealing action is about 3 feet (about 1 meter);
3) The cost to obtain the gravity based external force for grout sealing is almost zero, in contrast with the very high cost for inflatable packers, as well as with the other two types of passive grout seals, which require extra fiber reinforcement at a considerable cost.
Based on the discussions above, all the different types of subsea grout seals, including the ones for offshore jacket installations and the ones for offshore wind turbine structure installations, face the same challenges as how to achieve and maintain system overall reliability, what kind external force to be used for a grout sealing action, how to handle different sizes of the annular gaps, how to make it easy for transportation & installation of grout seals, and how to reduce system overall costs. In this disclosure, a simple, reliable and inexpensive subsea grout seal system is disclosed for all types of offshore structure installations, including both jacket installations and wind turbine structure installations, and particularly this new type of grout seal is able to overcome a wide range of annular gap sizes.